Begin by preparing the shortbread dough. Since it requires chilling, it’s best to start here! Preheat your oven to 350°F (175°C) and line two large baking sheets with parchment paper or Silpat mats. Set them aside. Using a pastry cutter or electric mixer, combine 1 cup softened butter, 2 cups flour, 1/2 cup powdered sugar, and 1/2 teaspoon fine salt. Initially, the mixture may look crumbly but will come together into a soft dough as you continue mixing. If it seems too dry, gently warm it in the microwave for 2–3 seconds to soften the butter—be careful not to melt it. Roll the dough into a 12-inch log, wrap tightly in plastic wrap, and chill in the refrigerator for about an hour or until firm; this will make slicing easier. Using a sharp knife, cut the log into 24 slices about 1/2 inch thick and place them on the prepared baking sheets, spaced 1 inch apart. Prick each cookie several times with a fork and bake one sheet at a time for 9–11 minutes, rotating halfway for even baking. Allow the cookies to cool fully on the pan placed on a wire rack.

While the cookies chill and bake, prepare the caramel filling so it has time to cool and thicken before topping. In a heavy saucepan over medium heat, combine 1 can sweetened condensed milk, 1/2 cup butter, 1/2 cup packed light brown sugar, 1/4 cup light corn syrup, and 1/2 teaspoon fine salt. Stir frequently as the mixture heats and just begins to bubble—if using a candy thermometer, cook until it reaches 212°F (100°C). The bubbling will start around the edges of the pan. Reduce the heat to low and let the caramel simmer, stirring often, until it thickens to a medium caramel color, about 10 minutes. To test, drag a spatula through the caramel and watch for the pan bottom to be visible for a moment. Remove from heat and stir in 1 teaspoon vanilla extract. Transfer to a container and let cool to room temperature. This caramel can be made ahead and stored covered at room temperature overnight or refrigerated for up to one week. If refrigerated, gently warm it in the microwave in 10-second bursts until soft enough to spread.

For the luscious dark chocolate ganache, heat 3/4 cup plus 3 tablespoons heavy cream in a microwave-safe bowl for about 45 seconds until it starts to bubble lightly. Pour 1 1/4 cups dark chocolate chips (60-65% cocoa) into the cream, ensuring they are fully submerged. Let the mixture sit for 1 minute, then stir gently until smooth. If using milk chocolate instead, heat 1/2 cup heavy cream and combine with 2 cups milk chocolate chips. If needed, heat the ganache an additional 15 seconds to melt any remaining chocolate bits and stir well. Mix in 3 tablespoons softened unsalted butter, 1 tablespoon light corn syrup (optional), and 1/4 teaspoon fine salt until fully combined. Cover the ganache with plastic wrap to prevent a skin from forming and allow it to cool to room temperature. To speed cooling, pour the ganache into a shallow pan. This can be prepared ahead and refrigerated for up to a month.

Optional, but recommended, is to transfer the cooled ganache to a piping bag fitted with a small French tip to pipe elegant swirls atop the cookies. Alternatively, spread it evenly over the caramel with a spoon or offset spatula.

Once the shortbread cookies are completely cooled, spread about 1 tablespoon of the room-temperature caramel onto each cookie. Pipe or spread the cooled chocolate ganache over the caramel layer. Finish by sprinkling each cookie with flaky sea salt and a touch of edible gold leaf for a glamorous touch. These cookies can be stored in an airtight container at room temperature for up to 2 days or refrigerated for up to 5 days. If the caramel appears to ooze or flow over the edges—a sign it may be slightly undercooked—store the cookies in the fridge to help firm the caramel and keep it in place.